Speaker: Wei Jiang

Beijing Computational Science Research Center    

Abstract: In the first part of the talk, we will talk about modeling and simulations for solid-state dewetting problems. We propose a phase field model for simulating solid-state dewetting and the morphological evolution of patterned islands on a substrate. The evolution is governed by the Cahn-Hilliard equation with isotropic surface tension and variable scalar mobility. The proposed approach easily deals with the complex boundary conditions arising in the solid-state dewetting problem. Since the method does not explicitly track the moving surface, it naturally captures the topological changes that occur during film/island morphology evolution. The numerical method is based on the cosine pseudospectral method together with a highly efficient, stabilized, semi-implicit algorithm. Numerical results on solid-state dewetting in two dimensions (2D) demonstrate the excellent performance of the method, including stability, accuracy and numerical efficiency. The method was easily extended to three dimensions (3D), with no essential difference from the 2D algorithm. Numerical experiments in 3D demonstrate the ability of the model to capture many of the complexities that have been observed in the experimental dewetting of thin films on substrates and the evolution of patterned islands on substrates.

In the second part, we will talk about the computer-aided design for progressive-addition lenses (PALs). PALs are often used to treat presbyopia, which is a very common phenomenon about human eyes when people become old. We proposed a variational-difference method for designing the optical free form surface of PALs. Compared with the existing literatures which solved the problem by B-spline finite element method, the essence of the proposed method lies in minimizing the functional directly by finite difference method rather than in approximating the solution of the corresponding Euler-Lagrange equation with respect to the functional. It is very easily understood and implemented by optical engineers, and meantime it can also produce satisfactory design results for optical engineers in less than several seconds.

Date&Time: November 23, 2012 (Friday), 14:30–15:30
Location: 606 Conference Room